Controllable-pitch centrifugal fan

ABSTRACT

A controllable-pitch centrifugal fan apparatus comprising a rotor system having a fan-blade assembly constraining a plurality of fan blades that are radially distributed by an equal distance to the rotor system&#39;s axis of rotation. Each fan blade is free to rotate about an axis of rotation fixed in the fan-blade assembly. A fan-blade pinion is affixed to each fan blade&#39;s axial extremity and has a gear profile capable of mating to a blade-pitch manipulating ring. This ring has a helical gear pattern affixed to its exterior cylindrical surface and a thread applied to an inner cylindrical cavity allowing it to threadedly mate to a pitch control base rigidly affixed to the fan-blade assembly concentrically with the plurality of fan blades. In its most optimal form, the blade-pitch manipulating ring consists of a ferromagnetic material subjected to fields generated by stator-born electromagnets in order to manipulate each fan blades pitch.

This application claims the benefit of application Ser. No. 15/424,831 filed 4 Feb. 2017.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The subject invention relates to an apparatus for a controllable-pitch centrifugal fan.

2. Description of the Prior Art

Centrifugal fan construction is well known in the prior art which includes a stator system containing a prime mover that is responsible for generating a rotational force. The rotor system and stator system are axially affixed and angularly coupled by a rotor-system coupling. The prime mover is controlled by an Electronic Control Unit (ECU) also affixed to the stator system. The rotor system contains a fan-blade assembly that contains and constrains a plurality of fan blades.

The prior art also discloses a fan-blade assembly having a plurality of fan blades being free to rotate about varying angles of rotation. Included in the prior art are varying means of controlling the angular position of the plurality of rotating fan blades in order to control the pitch of the fan blades while the fan-blade assembly is rotating.

SUMMARY OF THE INVENTION

The invention provides for a pitch control base being affixed rigidly to a fan-blade assembly and consisting of a cylindrical exterior having a fixed-pitch thread. The pitch control base is mounted concentrically with the plurality of fan blades in the fan-blade assembly which are radially distributed an equal distance from the axis of rotation of the fan-blade assembly. A blade-pitch manipulating mechanism having a hole with a thread of fixed pitch permitting it to mate with the thread of the pitch control base which are threadedly affixed to one another. The blade-pitch manipulating mechanism is capable of rotating independently of the fan-blade assembly through a profile constrained by the thread of the pitch control base when rotational forces are applied to it.

A pitch-actuating mechanism, affixed to the stator system, is responsible for imparting rotational forces on the blade-pitch manipulating mechanism. A plurality of pitch-manipulation transmission mechanisms is responsible for pairing the angular motion of the blade-pitch manipulating mechanism, with other pitch-manipulation transmission mechanisms, and ultimately with the fan blades in the plurality of blades as the blade-pitch manipulating mechanism travels the altitude of the thread of the pitch control base.

A method for achieving a controllable-pitch centrifugal fan includes applying a rotational force to a fan-blade assembly containing a plurality of fan blades surrounding a cavity in which a suction force is generated as a result of the rotation of these fan blades. This suction force draws in fluids in its vicinity which the plurality of fan blades then accelerates radially outward.

A rotational force from the pitch-actuating mechanism is paired to the blade-pitch manipulating mechanism which then transfers the rotational force exerted on it to each fan blade in the plurality of fan blades through a plurality of pitch-manipulation transmission mechanisms whose angular motion is coupled. The rotational forced exerted by the pitch-actuating mechanism on the blade-pitch manipulating mechanism is varied in order to position each fan blade in said plurality of fan blades to a commanded angular position in order to control the pitch and curvature of the plurality of fan blades the circumference of each of which has a fixed but varied curvature.

Advantages of the Invention

The invention in its broadest aspect employs the benefits of mechanical advantage introduced by a thread-and-screw-like actuating mechanism to control the pitch of fan blades in a rotating centrifugal fan. More specific instantiations of the broadest claim employs electromagnets which are responsible for actuating the thread-and-screw-like actuating mechanism which allows the rotor and stator system to avoid mechanical coupling that would introduce undesirable drag-related inefficiencies. The proposed mechanism is very simple and will result in low manufacturing costs.

Beyond these advantages of the prior art, the benefits of controllable-pitch fan technology are achieved—foremost of which is the ability to achieve variable air volume (VAV).

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is perspective view of the controllable-pitch, controllable-curvature centrifugal fan.

FIG. 2 is an exploded view of the controllable-pitch, controllable curvature centrifugal fan.

FIG. 3 is an exploded view of the fan-blade assembly containing the fan blade, fan blade cap, and fan-blade pinion.

FIG. 4A is an orthogonal view of the fan-blade pinion and FIG. 4B is a perspective view of the same.

FIG. 5A is an orthogonal view of the pitch control base and fan blade assembly and FIG. 5B is a perspective view of the same.

FIG. 6A is a perspective view of the lower fan assembly and FIG. 6B is a perspective view of the same.

FIG. 7A is an orthogonal view of the assembly connector and FIG. 7B is a perspective view of the same.

DESCRIPTION OF THE ENABLING EMBODIMENT

Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, an apparatus for a controllable-pitch centrifugal fan constructed in accordance with the subject invention is shown in FIGS. 1 through 7.

The controllable-pitch centrifugal fan is comprised of a generalized stator system (20), containing a prime mover (30) responsible for generating a rotational force having a fixed axis of rotation as applied to a generalized rotor system. The stator system (20) also hosts an Electronic Control Unit (ECU (32)) which is responsible for controlling the forces generated by the prime mover (30) through wires connecting the two.

A rotor-system coupling (23) pairs the angular motion and affixes the axial positions of the prime mover (30) and the rotor system with respect to one another. The rotor system contains a fan-blade assembly containing and constraining a plurality of fan blades (26B). The complete fan-blade assembly consists of a lower fan assembly (27C), responsible for constraining the lower end of each fan blade (26B), and connectors joining the lower assembly with the rest of the fan assembly; this is shown in the figures as one possible means of manufacturing these details of the fan assembly not core to this invention. Another such detail is shown in the fan blade cap (26C) which aids the lower fan assembly (27C) to support the fan blades (26B).

Each blade in the plurality of fan blades (26B) has a convex curvature on one side and concave curvature on the other side both of which are fixed along the length of the fan blade's (26B) rotational axis. Each blade is free to rotate an arbitrary angle about its own independent axis of rotation. The blades are equally distributed with a radial measure about the axis of rotation of the prime mover (30).

A pitch control base (27A) is rigidly affixed to the fan-blade assembly and consists of a cylindrical exterior surface, concentric with the plurality of fan blades (26B), with a fixed-pitch thread. The pitch control base (27A) has a blade-pitch manipulating ring (25) mounted on its thread via an inner cylindrical cavity in the blade-pitch manipulating ring (25) having a diameter and fixed thread permitting this mating. The blade-pitch manipulating ring (25) has a magnetic composition (24) as a result of a constituent material onto which a magnetic field can impart a motion-inducing force. The exterior curved surface of the blade-pitch manipulating ring (25) has a helical gear pattern affixed thereto with the axis of the helix being coaxial with that of the blade-pitch manipulating ring (25).

A fan-blade pinion (26A) is axially affixed to each fan blade (26B) in the plurality of fan blades (26B). The fan-blade pinions (26A) have a diameter and gear-tooth profile capable of mating with the rotational and axial motion of the helical gear arrangement of the blade-pitch manipulating ring (25). Each fan-blade pinion (26A) is tangentially mated to the blade-pitch manipulating ring (25) in order to tie the rotational motion of each. Also, each fan-blade pinion (26A) is angularly coupled with the fan blade (26B) onto which they are affixed.

An advancing electromagnet (22) generates an electromagnetic force applied to the blade-pitch manipulating ring (25) to cause it to accelerate in the direction of rotation of the fan-blade assembly. This electromagnet has physical dimensions and is affixed to the stator system (20) such that its electromagnetic field is capable of applying a force on the magnetic composition (24) of the blade-pitch manipulating ring (25) throughout the entire travel of the blade-pitch manipulating ring (25) as the blade-pitch manipulating ring (25) traverses the altitude of the pitch control base (27A). It is disposed so as not to impede the rotation of the fan-blade assembly and is wired to the ECU (32).

Similarly, a retarding electromagnet (28) generates an electromagnetic force applied to the blade-pitch manipulating ring (25) to cause it to accelerate in the direction of rotation opposite to that of the fan-blade assembly. This electromagnet has physical dimensions and is affixed to the stator system (20) such that the electromagnetic field from the retarding electromagnet (28) is capable of applying a force on the magnetic composition (24) of the blade-pitch manipulating ring (25) throughout the entire travel of the blade-pitch manipulating ring (25) as the blade-pitch manipulating ring (25) traverses the altitude of the pitch control base (27A). It is disposed so as not to impede the rotation of the fan-blade assembly and is wired to the ECU (32).

A position sensor (21), capable of measuring the position of the blade-pitch manipulating ring (25), transfers measured position values to the ECU (32) via wires joining the ECU (32) and the position sensor (21).

A method for a controllable-pitch centrifugal fan involving the application of a rotational force to a fan-blade assembly containing a plurality of fan blades surrounding a cavity in which a suction force is generated as a result of the rotation of these fan blades. This suction force draws in fluids in its vicinity which the plurality of fan blades then accelerates radially outward.

The method involves applying magnetic forces generated by a plurality of electromagnets to the blade-pitch manipulating ring (25) that is constituted of materials lacking magnetic polarization but which are attracted to these magnetic forces. The rotation induced by the magnetic forces on the blade-pitch manipulating ring is transferred to the plurality of fan blades through mating gears of the blade-pitch manipulating ring and fan-blade pinions.

The method involves applying magnetic forces to accelerate the rotation of the blade-pitch manipulating ring relative to and in the direction of rotation of the fan-blade assembly with an advancing electromagnet. Conversely, forces to accelerate the rotation of the blade-pitch manipulating ring relative to and in the opposing direction of rotation of the fan-blade assembly are accomplished by a retarding electromagnet.

The magnitude of the magnetic forces generated by the advancing and retarding electromagnets is varied in accordance with the well-known proportional-integral-derivative (PID) control algorithm in order to control the pitch and curvature of the plurality of fan blades by manipulating the angular position of each fan blade by using the known relation between fan blade angle and the position of the blade-pitch manipulating ring (25) along the altitude of the pitch control base (27A) as measured by a position sensor. Current is limited to the advancing and retarding electromagnets so as to only apply current to one of the electromagnets using a dead-band strategy having a range about the commanded fan-blade-pitch setpoint in which current is not applied to the electromagnets when the pitch of said plurality of fan blades is within this range.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings and may be practiced otherwise than as specifically described while within the scope of the appended claims. That which is prior art in the claims precedes the novelty set forth in the “characterized by” clause. The novelty is meant to be particularly and distinctly recited in the “characterized by” clause whereas the antecedent recitations merely set forth the old and well-known combination in which the invention resides. These antecedent recitations should be interpreted to cover any combination in which the inventive novelty exercises its utility. The use of the word “said” in the apparatus claims refers to an antecedent that is a positive recitation meant to be included in the coverage of the claims whereas the word “the” precedes a word not meant to be included in the coverage of the claims. In addition, the reference numerals in the claims are merely for convenience and are not to be read in any way as limiting.

ELEMENT LIST Element Symbol Element Name 20 stator system 21 position sensor 22 advancing electromagnet 23 rotor-system coupling 24 magnetic composition 25 blade-pitch manipulating ring 28 retarding electromagnet 30 prime mover 32 ECU 34 blade-pitch manipulating mechanism 26A fan-blade pinion 26B fan blade 26C fan blade cap 27A pitch control base 27B fan blade assembly 27C lower fan assembly 27D Assembly Connector 

What is claimed is:
 1. An apparatus for a controllable-pitch centrifugal fan including, a fan-blade assembly, a plurality of fan blades (26B) being contained and constrained by said fan-blade assembly—each fan blade (26B) in said plurality of fan blades (26B) being free to rotate, a stator system (20) generating a rotational force paired to said fan-blade assembly causing said fan-blade assembly to rotate, and characterized by, a pitch control base (27A) being affixed rigidly to said fan-blade assembly and consisting of a cylindrical exterior having a fixed-pitch thread, a blade-pitch manipulating mechanism (34) having a hole with a thread of fixed pitch permitting said blade-pitch manipulating mechanism (34) to mate with the thread of said pitch control base (27A), being mounted with mating threads on said pitch control base (27A), and being capable of rotating independently of said fan-blade assembly through a profile constrained by said thread of said pitch control base (27A) when rotational forces are applied to said blade-pitch manipulating mechanism (34), a pitch-actuating mechanism imparting rotational forces on said blade-pitch manipulating mechanism (34) when said blade-pitch manipulating mechanism (34) is mounted along said thread of said pitch control base (27A), and being affixed to said stator system (20), a plurality of pitch-manipulation transmission mechanisms pairing the angular motion of said blade-pitch manipulating mechanism (34) with others of said pitch-manipulation transmission mechanisms and ultimately pairing the angular motion of said blade-pitch manipulating mechanism (34) to fan blades (26B) in said plurality of blades as said pitch-controlling mechanism travels the altitude of the thread of said pitch control base (27A).
 2. An apparatus for a controllable-pitch centrifugal fan as set forth in claim 1 including, an Electronic Control Unit (ECU (32)) affixed rigidly to said stator system (20), a position sensor (21) being affixed rigidly to said stator system (20) and being wired to said ECU (32), and characterized by, said position sensor (21) having dimensions and being disposed so as to permit the measurement of the position of said blade-pitch manipulating mechanism (34) with respect to its travel along the altitude of said pitch control base (27A).
 3. An apparatus for a controllable-pitch centrifugal fan as set forth in claim 1 including, a ferromagnetic component comprising a portion of the constitution of said blade-pitch manipulating mechanism (34) and consisting of a material onto which a magnetic field can impart a motion-inducing force, an Electronic Control Unit (ECU (32)) affixed rigidly to said stator system (20), a plurality of electromagnets (22, 28) each of which consisting of a plurality of windings of an electric current carrying material, said windings of which being wired to said ECU (32), and being affixed to said stator system (20), and characterized by, said plurality of electromagnets (22, 28) acting as said pitch-actuating mechanism, each electromagnet in said plurality of electromagnets (22, 28) being disposed in relation to said blade-pitch manipulating mechanism (34) so as to impart a magnetic force onto said ferromagnetic component of said blade-pitch manipulating mechanism (34) capable of modulating the angular rotation of said blade-pitch manipulating mechanism (34) as said blade-pitch manipulating mechanism (34) rotates with said fan-blade assembly and traverses the altitude of said pitch control base (27A), and being disposed so as not to impede the rotation of said fan-blade assembly.
 4. An apparatus for a controllable-pitch centrifugal fan as set forth in claim 3 including, said ferromagnetic component being comprised of a material having a magnetic polarization, and characterized by, said plurality of electromagnets (22, 28) having reversible polarity and being disposed so as to modulate the angular rotation of said blade-pitch manipulating mechanism (34) in both clock-wise and anticlockwise angular directions.
 5. An apparatus for a controllable-pitch centrifugal fan as set forth in claim 3 including, said ferromagnetic component being comprised of a material lacking a magnetic polarization but capable of being accelerated by a magnetic force, and characterized by, a set of advancing electromagnets (22) in said plurality of electromagnets (22, 28) being disposed so as to be capable of generating an electromagnetic force applied to said blade-pitch manipulating ring (25) to cause said blade-pitch manipulating ring (25) to accelerate in the direction of rotation relative to that of said fan-blade assembly, a set of retarding electromagnets (28) in said plurality of electromagnets (22, 28) being disposed so as to be capable of generating an electromagnetic force applied to said blade-pitch manipulating ring (25) to cause said blade-pitch manipulating ring (25) to accelerate in the opposite direction of rotation relative to that of said fan-blade assembly.
 6. An apparatus for a controllable-pitch centrifugal fan as set forth in claim 1 including, an axis of rotation of said stator system's (20) rotational force paired to said fan-blade assembly, said plurality of fan blades (26B) being distributed equally in said fan-blade assembly with respect to a radial measure about said fan-blade assembly's axis of rotation and about a plane perpendicular to said fan-blade assembly's axis of rotation, and characterized by, said pitch control base (27A) having a threaded-exterior cylindrical surface being coaxial with said plurality of fan blades (26B) and being affixed rigidly to said fan-blade assembly, said blade-pitch manipulating ring (25) having an exterior cylindrical surface with a fixed radius, being coaxial with said internal inner cavity of said blade-pitch manipulating ring (25), having a helical gear pattern mounted on the exterior cylindrical surface of said blade-pitch manipulating ring (25) the helical axis of which being coaxial with the axis of said blade-pitch manipulating ring (25), said pitch-manipulation transmission mechanisms consisting of gears connected in a series of stages from said blade-pitch manipulating ring (25) to each fan blade (26B) in said plurality of fan blades (26B), being tangentially juxtaposed to one another having parallel axes of rotation, being free to rotate, being attached rigidly to said fan-blade assembly, and having a multitude of measures of diameter and gear teeth the selection of which permitting the reduction or increase of angular force and speed produced by each stage to subsequent stages, the first stage of said pitch-manipulation transmission mechanisms being capable of mating with the helical gear pattern of said blade-pitch manipulating ring (25) as said blade-pitch manipulating ring (25) rotates and traverses the altitude of the thread of said pitch control base (27A), stages subsequent to said first stage being capable of mating tangentially to earlier and later stages in order to transfer angular rotation from one stage to the next stage ultimately to each fan blade (26B) in said plurality of fan blades (26B).
 7. An apparatus for a controllable-pitch centrifugal fan as set forth in claim 6 having a plurality of fan-blade pinions (26A), comprising the pitch-manipulation transmission mechanism, each fan-blade pinion (26A) of which being axially affixed to each fan blade (26B) in said plurality of fan blades (26B), having a diameter and gear-tooth profile capable of mating with the rotational and axial motion of said helical gear arrangement of said blade-pitch manipulating ring (25), being tangentially mated to said blade-pitch manipulating ring (25), and being angularly coupled with said fan blade (26B),
 8. An apparatus for a controllable-pitch centrifugal fan as set forth in claim 1 where each fan blade (26B) in said plurality of fan blades (26B) has an axis of rotation parallel with said axis of rotation of said prime mover (30).
 9. An apparatus for a controllable-pitch centrifugal fan as set forth in claim 8 where each fan blade (26B) in said plurality of fan blades (26B) has a curvature varying about the circumference of said fan blade (26B) in a plane orthogonal to said axis of rotation of said fan blade (26B).
 10. An apparatus for a controllable-pitch centrifugal fan as set forth in claim 9 each fan blade (26B) in said plurality of fan blades (26B) having a convex curvature on one side of said fan blade (26B) and concave curvature on the opposite side both of which are fixed along the length of said fan blade (26B)'s axis of rotation.
 11. An apparatus for a controllable-pitch centrifugal fan comprising; a stator system (20), a prime mover (30) being part of a stator system (20) and generating a rotational force having a fixed axis of rotation, an Electronic Control Unit (ECU (32)) affixed to said stator system (20) controlling the forces generated by said prime mover (30) through wires connecting the two, a fan-blade assembly, being part of said rotor system, containing and constraining a plurality of fan blades (26B) each fan blade (26B) of which being free to rotate, each blade in said plurality of fan blades (26B) having a convex curvature on one side of said fan blade (26B) and concave curvature on the opposite side being fixed along the length of said fan blade (26B)'s rotational axis, a rotor-system coupling (23) pairing the angular motion and affixing the axial positions of said prime mover (30) and said rotor system with respect to one another, and characterized by, each fan blade (26B) in said plurality of fan blades (26B) being free to rotate about its own independent axis of rotation through an arbitrary angle, and being equally distributed with a radial measure about said axis of rotation of said prime mover (30), a pitch control base (27A) consisting of a cylindrical exterior, concentric with said plurality of fan blades (26B), having a fixed-pitch thread and being affixed rigidly to said fan-blade assembly, a blade-pitch manipulating ring (25) consisting of a cylindrical ring having an inner cylindrical cavity with a diameter and fixed thread permitting said blade-pitch manipulating ring's (25) mating to said pitch control base (27A), mounted on said pitch control base (27A) by threads mating together all the while permitting axial motion of said blade-pitch manipulating ring (25) as a result of said threading and any rotational forces applied to said blade-pitch manipulating ring (25), and having a magnetic composition (24) including a material onto which a magnetic field can impart a motion-inducing force but said magnetic composition (24) lacking a magnetic polarization, the exterior curved surface of said blade-pitch manipulating ring (25) having a helical gear pattern affixed thereto with the axis of the helix being coaxial with that of said blade-pitch manipulating ring (25), a plurality of fan-blade pinions (26A) each fan-blade pinion (26A) of which being axially affixed to each fan blade (26B) in said plurality of fan blades (26B), said fan-blade pinions (26A) having a diameter and gear-tooth profile capable of mating with the rotational and axial motion of said helical gear arrangement of said blade-pitch manipulating ring (25), being tangentially mated to said blade-pitch manipulating ring (25) in order to tie the rotational motion of each, and being angularly coupled with said fan blade (26B) onto which each fan-blade pinion (26A) is affixed, an advancing electromagnet (22) generating an electromagnetic force applied to said blade-pitch manipulating ring (25) to cause it to accelerate in the direction of rotation of said fan-blade assembly, having physical dimensions and being affixed to said stator system (20) such that the electromagnetic field from said advancing electromagnet (22) is capable of applying a force on said magnetic composition (24) of said blade-pitch manipulating ring (25) throughout the entire travel of said blade-pitch manipulating ring (25) as said blade-pitch manipulating ring (25) traverses the altitude of said pitch control base (27A), being disposed so as not to impede the rotation of said fan-blade assembly, and being wired to said ECU (32), a retarding electromagnet (28) generating an electromagnetic force applied to said blade-pitch manipulating ring (25) to cause it to accelerate in the direction of rotation opposite to that of said fan-blade assembly, having physical dimensions and being affixed to said stator system (20) such that the electromagnetic field from said retarding electromagnet (28) is capable of applying a force on said magnetic composition (24) of said blade-pitch manipulating ring (25) throughout the entire travel of said blade-pitch manipulating ring (25) as said blade-pitch manipulating ring (25) traverses the altitude of said pitch control base (27A), being disposed so as not to impede the rotation of said fan-blade assembly, and being wired to said ECU (32), a position sensor (21) being capable of measuring the position of said blade-pitch manipulating ring (25) whose measured values are conferred to said ECU (32) via wires joining said ECU (32) and said position sensor (21).
 12. A method for a controllable-pitch centrifugal fan including: applying a rotational force to a fan-blade assembly containing a plurality of fan blades (26B) generating a suction force in the cavity between said plurality of fan blades (26B) on a fluid in the vicinity of said cavity that is consequently accelerated outward radially by said plurality of fan blades (26B), said method characterized by, applying a rotational force from a stator-born pitch-actuating mechanism to a blade-pitch manipulating mechanism (34), said blade-pitch manipulating mechanism (34) having a cylindrical cavity with a diameter and thread allowing said blade-pitch manipulating mechanism (34) to mount with mating threads onto threads of a cylindrical pitch control base (27A) that is rigidly affixed to said fan-blade assembly, transferring the rotational force exerted by said pitch-actuating mechanism on said blade-pitch manipulating mechanism (34) to each fan blade (26B) in said plurality of fan blades (26B) through a plurality of pitch-manipulation transmission mechanisms whose angular motion is coupled with said blade-pitch manipulating mechanism (34), ultimately coupled rotationally to fan blades (26B) in said plurality of fan blades (26B), varying said rotational force from said pitch-actuating mechanism in order to position fan blades (26B) in said plurality of fan blades (26B) to a commanded angular position in order to control the pitch and curvature of said plurality of fan blades (26B) the circumference of which has a fixed but varied curvature.
 13. A method for a controllable-pitch centrifugal fan as set forth in claim 12 applying said rotational force from said pitch-actuating mechanisms, where said rotational force is caused by a magnetic force generated by a plurality of electromagnets (22, 28) acting as said pitch-actuating mechanisms, to a blade-pitch manipulating ring (25) acting as said blade-pitch manipulating mechanism (34), said blade-pitch manipulating ring (25) being constituted of materials susceptible to said magnetic force of said plurality of electromagnets (22, 28).
 14. A method for a controllable-pitch centrifugal fan as set forth in claim 13 applying a magnetic force to said blade-pitch manipulating ring (25) consisting of a material which is purely attracted to said magnetic force, i.e. a material that lacks its own magnetic polarization, by said plurality of electromagnets (22, 28) some of which act as advancing electromagnets (22) causing magnetic forces tending to accelerate said blade-pitch manipulating ring (25) in the direction of rotation of said rotating fan-blade assembly, other electromagnets (22, 28) in said plurality of electromagnets (22, 28) which act as retarding electromagnets (28) causing magnetic forces tending to accelerate said blade-pitch manipulating ring (25) in the opposite direction of rotation of said rotating fan-blade assembly.
 15. A method for a controllable-pitch centrifugal fan as set forth in claim 14 limiting current applied to said advancing and retarding electromagnets (22, 28) where current is never applied to advancing and retarding electromagnets (22, 28) at the same time.
 16. A method for a controllable-pitch centrifugal fan as set forth in claim 13 varying the magnitude of said magnetic force to manipulate the pitch of each fan blade (26B) in said plurality of fan blades (26B) to a desired position by varying the magnitude of current applied by said electromagnets (22, 28).
 17. A method for a controllable-pitch centrifugal fan as set forth in claim 16 varying the magnitude of said magnetic force in accordance with the proportional-integral-derivative (PID) control algorithm with feedback from a position sensor (21) measuring the position of said blade-pitch manipulating ring (25) along the altitude of said pitch control base (27A).
 18. A method for a controllable-pitch centrifugal fan including: applying a rotational force to a fan-blade assembly containing a plurality of fan blades (26B) generating a suction force in the cavity between said plurality of fan blades (26B) on a fluid in the vicinity of said cavity that is consequently accelerated outward radially by said plurality of fan blades (26B), said method characterized by, applying magnetic forces generated by a plurality of electromagnets (22, 28) to a blade-pitch manipulating ring (25) that is constituted of materials lacking magnetic polarization but which are attracted to said magnetic forces, said blade-pitch manipulating ring (25) having a cylindrical cavity with a diameter and thread allowing said blade-pitch manipulating ring (25) to mount with mating threads onto threads of a cylindrical pitch control base (27A) that is rigidly affixed to said fan-blade assembly, said rotation induced by said magnetic forces on said blade-pitch manipulating ring (25) being transferred to said plurality of fan blades (26B) through a helical gear pattern mounted on the exterior cylindrical surface of said blade-pitch manipulating ring (25) tangentially mated with a plurality of fan-blade pinions (26A) having a gear tooth profile capable of mating with the axial and rotational motion of said helical gearing of said blade-pitch manipulating ring (25) with a fan-blade pinion (26A) being affixed axially and coupled angularly with each fan blade (26B), applying said magnetic forces to accelerate the rotation on said blade-pitch manipulating ring (25) relative to and in the direction of rotation of said fan-blade assembly with an advancing electromagnet (22), applying forces to accelerate the rotation on said blade-pitch manipulating ring (25) relative to and in the opposing direction of rotation of said fan-blade assembly with a retarding electromagnet (28), varying the magnitude of the magnetic forces generated by said advancing and retarding electromagnets (22, 28) in accordance with the proportional-integral-derivative (PID) control algorithm in order to control the pitch and curvature of said plurality of fan blades (26B) the angular position of which is inferred by the known relation between fan blade (26B) angle and the position of said blade-pitch manipulating ring (25) along the altitude of said pitch control base (27A) as measured by a position sensor (21), limiting the current to said advancing and retarding electromagnets (22, 28) so as to only apply current to one of said electromagnets (22, 28) using a dead-band strategy having a range about the commanded fan-blade pitch setpoint in which current is not applied to said electromagnets (22, 28) when the pitch of said plurality of fan blades (26B) is within said range. 